A conventional circular knitting machine generally has a needle selected device to form jacquard patterns on the surface of knitting fabrics. Through the needle selected device, a knitting needle can be driven out or in to form a knitted area or an un-knitted area on the fabric. More specifically, the needle selected device includes a plurality of needle selected sheets. Each knitting needle is connected with a jacquard needle. The jacquard needle has a fulcrum latched on the knitting needle and a needle selected section extended from the fulcrum. The needle selected section has a rear end formed a needle foot movable in a track formed by at least one cam. The needle selected section includes a plurality of needle butts. When the needle selected device is moved away from the needle selected sheets, the needle foot can drive the knitting needles outwards to hook and pull a yarn to form a yarn loop according to the track formed by the cam. While the needle selected device drives any one of the needle selected sheets to push the needle butts, the jacquard needle is pushed to escape from the cam, so that the knitting needle cannot be moved out to do knitting. Hence whether a knitting pattern is formed depends on whether the jacquard needle is being pushed by the needle selected device to escape from the cam. The jacquard needle is not driven by the cam, so that the knitting needle cannot be pushed out to do knitting.
To improve return mechanism of the jacquard needle, Applicant submitted a patent application in 1997 at R.O.C. patent No. 435457 entitled: “Circular knitting machine computer jacquard needle selected sheet automatic return apparatus”. The highlight is depicted in its abstract as follow: “A circular knitting machine computer jacquard needle selected sheet automatic return apparatus allows a needle selected sheet to automatically return to the path of a needle-pushing cam after being pushed downwards by a needle selected foot. The needle selected sheet has a return apparatus at a back side on a desired location. The return apparatus has an arched portion at one end butting an inner wall of an upper needle dial. After the needle selected sheet is pushed downwards by the needle selected foot of the needle selected device, the needle foot of the needle selected sheet escapes from the path of the needle-pushing cam. Meanwhile, the gap formed between the back side of the needle selected sheet and the return apparatus shrinks, and the needle selected sheet does not push the sinker outwards. Hence the yarn hooked and pulled by the knitting needle cannot form a yarn loop. After the needle foot of the needle selected sheet has slid over by the surface of the cam portion of the needle-pushing cam, the elasticity of the return apparatus pushes the needle foot back to the path of the needle-pushing cam”. As mentioned in the aforesaid abstract, the needle selected sheet is driven by the needle-pushing cam in normal conditions so that the knitting needle at the front end of the needle selected sheet hooks and pulls a yarn to form a yarn loop, or at least one needle selected sheet is pushed by the needle selected device to escape from the needle-pushing cam, so that the knitting needle cannot be driven by the needle selected sheet to form the yarn loop. More specifically, the needle selected sheet has the return apparatus that is an elastic plate, an elastic rod or an elastic strut butting the upper needle dial to provide an automatic returning force for the needle butts of the needle selected sheet.
However, R.O.C. patent No. 435457 mentioned above has some drawbacks in practice. First, the return apparatus is located on the needle foot of the jacquard needle, this limits the length of the return apparatus, and it also creates a longer movement distance when the jacquard needle is moved downwards. The longer movement distance of the return apparatus results in a greater stress it has to withstand. Since the interior space of a circular knitting machine is limited, the thickness of the return apparatus is difficult to increase, thus the lifespan of the return apparatus also is shorter. Moreover, the longer movement distance of the return apparatus also results in greater elastic force pushing the needle foot of the jacquard needle to return, and impact of the needle foot on the cam also is greater, this easily damages the jacquard needle after using for a long-term period of time.
Damage of the jacquard needle creates obvious defects on the knitted fabrics. As the circular knitting machine is quite bulky and consists of a great number of elements, it is difficult to inspect and identify the damaged elements, hence there is still room for improvement in terms of overcoming the wearing and loss problems caused by the return apparatus.